The Repetition Mechanism
The repetition mechanism is (as its name suggests) the part of the escapement action that allows the piano to quickly repeat a note without having to completely reset the action to its original position. The repetition lever accomplishes this by using a spring to push the hammer back into position, allowing the jack to reset under the hammer knuckle.
The repetition lever, also called the balancier, (1) is attached to the
wippen - When the key is depressed by the pianist, the wippen is raised, which in turn raises the repetition lever and jack. The repetition lever pushes up on
the hammer, until the leather pad (2) on the top of the repetition lever comes into contact with the drop screw. At this same point, the jack comes into contact with the
let-off button and is rotated from under the hammer knuckle
and stops against the jack stop felt (3) which is affixed to the bottom of the repetition lever. When the hammer hits the string and
rebounds in the opposite direction, the hammer knuckle forces the repetition lever downward, rotating the lever on the repetition lever flange
(4) and compressing the repetition spring (5). When the key is partially released, this spring pushes the repetition lever back up, pushing
the hammer back into position for a repeated strike. When at rest, the repetition lever is held at the proper position by the repetition lever
regulating button (6), which has a felt pad (7) that rests against the wippen. The position of the repetition lever can be precisely
adjusted with the repetition lever regulating screw (8).
Follow the link to watch an animation of the repetition mechanism in action...